In recent years, in the fields of photoresist, adhesion, coating, and the like, the research and development of a photocuring method for curing various resin compositions by using a photobase generator have been vigorously carried out. As a resin composition curing system using a photobase generator, a method of curing a compound having an epoxy group is known (for example, Non-Patent Literature 1). In the curing system of the compound having an epoxy group, by applying the phenomenon in which the compound having an epoxy group is cured by causing a crosslinking reaction by the action of a base, the irradiation of light (active energy rays) is performed to generate a base from a photobase generator in the resin composition comprising the compound having an epoxy group, and then a heating treatment is performed to cure the compound having an epoxy group. In addition, a method is also known in which a photobase generator generating a strong base such as amidine, guanidine, biguanide, or phosphazene, a compound having an epoxy group, and, for example, a crosslinking agent having an acidic proton such as a polyfunctional thiol are used in combination such that the compound having an epoxy group and the crosslinking agent are rapidly cured at a low temperature (for example, Patent Literature 1 and Non-Patent Literature 2 and 3).
As a resin composition curing system using a general base, a sol-gel method by the hydrolysis and the polycondensation of a silane coupling agent having alkoxysilyl groups is known. During the hydrolysis by a base, in a case where one alkoxysilyl group is hydrolyzed to become a silanol group, steric hindrance is reduced, and accordingly, the remaining alkoxysilyl groups can be easily hydrolyzed to become silanol groups. Accordingly, because the polycondensation proceeds in the presence of more silanol groups having high polarity than in a case where an acid is used, the insolubilization of gel easily occurs, and clouding and precipitation easily occur before the molecular weight increases. In a case where the silanol group and the base form a salt and are precipitated at this time, the base is driven out of the reaction system, and accordingly, a problem in that the silane coupling agent as a raw material remains occurs. Therefore, in the sol-gel method using a base, generally, a method is used in which first the silane coupling agent having alkoxysilyl groups is heated together with water or an acid catalyst is caused to act such that the alkoxysilyl groups are partially hydrolyzed and polycondensed, and then the remaining silanol groups are polycondensed by adding a base such that the silane compound is cured (Non-Patent Literature 4).
As the sol-gel method, for example, a method is known in which a silane coupling agent having alkoxysilyl groups is heated in advance by adding water thereto to prepare a resin composition comprising a silane compound in which the alkoxysilyl groups are partially hydrolyzed and polycondensed, a photobase generator is added to the resin composition, and then the resin composition is irradiated with light (active energy rays) to generate a base from the photobase generator and polycondense the remaining alkoxysilyl groups or silanol groups (for example, Patent Literature 2). Because the sol-gel method is started by heating before the irradiation of light (active energy rays), the hydrolysis and the polycondensation can be finished in a desired state. However, because heating needs to be performed for a long period of time for preparing the resin composition, and the molecular weight of the resin easily increases, the sol-gel method is unstable, and the pot life of the resin composition is easily shortened.
In addition, for example, a method is known in which a sol-gel method and photo-radical polymerization are allowed to simultaneously proceed by using a polymer obtained by partially hydrolyzing and polycondensing a silane coupling agent having a methacryl group and using a photobase generator and a photo-radical generator in combination (for example, Non-Patent Literature 5). However, because the photobase generator and the photo-radical generator described in Non-Patent Literature 5 are oil-soluble and have low affinity (solubility) with a solvent such as water or an alcohol, a solvent imposing a high environmental load such as chloroform needs to be used. In addition, because the base generated from the photobase generator is a weak base such as a primary or secondary amine, the base has a problem in that the rate of hydrolysis or polycondensation is lower than that obtained by a strong base.
Meanwhile, a method is being examined in which a photoacid generator and a photo-radical generator are used in combination to cure a silane coupling agent having an acryl group by causing a sol-gel method and photo-radical polymerization to simultaneously proceed (for example, Non-Patent Literature 6). With the method of Non-Patent Literature 6, because a low-molecular weight monomer can be handled as it is, the pot life of a resin composition is long, and a polymer having high uniformity at a molecular level can be prepared. However, the strong acid generated from the photoacid generator has a problem in that curing consumes a long time or a metal may be corroded by the acid remaining in the resin. Furthermore, in the method of Non-Patent Literature 6, the silane coupling agent is hydrolyzed by the moisture in the atmosphere, which leads to problems in that the humidity control is difficult, the reproducibility is poor, the moisture in the atmosphere cannot easily permeate the inside of the resin composition, and curing failure easily occurs.
Therefore, for photocuring a silane compound (a silane coupling agent), a method which does not use a sol-gel method performed by only using light, that is, a method is mainly used in which hydrolysis and polycondensation of alkoxysilyl groups of the silane coupling agent are finished first by using an acid, and then the silane coupling agent is subjected to general photocuring (radical polymerization between acrylate compounds, an ene-thiol reaction between an allyl compound and a thiol compound, or cationic polymerization between epoxy compounds) (for examples, Non-Patent Literature 7 and 8, and Patent Literature 3).
In addition, as a composition using hydrolysis and polycondensation of a silane coupling agent having alkoxysilyl groups, a polysiloxane-based coating composition is known (for example, Patent Literature 4 and 5). In the coating composition described in Patent Literature 4, an alkali metal thiocyanate is used for hydrolysis and polycondensation of the silane coupling agent. In addition, in the coating composition described in Patent Literature 5, instead of the alkali metal thiocyanate, for example, an alkali metal salt of an organic carboxylic acid such as sodium acetate and acetic acid are used in combination. In a case where the alkali metal salt of an organic carboxylic acid and acetic acid are used in combination, the composition at the early stage of curing is slightly acidic because the amount of acetic acid is larger than that of the alkali metal salt of an organic carboxylic acid. However, after coating, due to the volatilization of acetic acid, the ratio of the existing alkali metal salt of an organic carboxylic acid becomes relatively high, and hence the composition becomes basic. It is considered that as a result, polycondensation can occur, and the pot life can be improved.